1. Field of the Invention
The field of the present invention relates to the preparation of fluxed bitumen-based binders mostly used for making road surface layers and/or road pavements and/or for civil engineering applications, and more particularly to the preparation of fluxing oils forming part of the composition of such binders by chemically modifying fatty substances of natural origin.
2. Description of the Related Art
The bitumen is the main hydrocarbon binder used in the field of road works and civil engineering. It may be used either pure or modified by polymer additions, where it is then called modified bitumen.
Bitumen used in road binders is excessively viscous at room temperature to be suitably handled or to have an adapted wettability as regards aggregates.
There are several means for making bitumen or modified bitumen handleable: it may be either heated depending on its viscosity, or brought in emulsion, or its viscosity may be reduced by mixing with solvents or “fluxing oils”. Most of these fluxing oils are derived from petroleum.
The bitumen recovers its initial properties, once in use, whatever the technique employed, respectively by cooling, by evaporating the water from emulsion or by evaporating the solvent. The latter alternative as a consequence causes volatile organic compounds to be released in the atmosphere, which is harmful to the environment and represents a wastage of the fossil energy.
Using fluxing agents, also called fluxing oils, based on vegetable and/or animal fatty substances (oils and fats) was already known, to thus prevent any volatile organic compound (VOCs) emission.
In general, raw fatty substances of natural origin have a good solvency for bitumen. On the contrary, they are highly viscous, which may be reduced by converting triglycerides into monoesters.
The French patent application FR 2 721 043 (VIALIT) describes a fluxing oil-containing bitumen emulsion, said emulsion comprising from 50 to 90% by weight of bitumen and from 1 to 50% by weight of a fluxing oil, together with a fatty amine- or organic silicon-based adhesion-promoting agent. The fluxing oil may be a vegetable oil such as rapeseed oil, a derivative thereof such as its fatty acid part, a combination of fatty acids, a transesterification product like a rapeseed oil methyl ester or a rapeseed oil alkyd resin derivative.
The French patent application FR 2 770 850 (ELF ANTAR FRANCE) describes a bitumen composition comprising a vegetable oil derived additive. Said additive is a residue from the distillation of such oil or a product resulting from transesterification of said oil with a C1 to C6 alkanol.
However, fatty substances of natural origin used in these applications do not possess a sufficient drying ability to succeed in polymerizing sufficiently rapidly with no catalyst, which does result in excessively soft binders which sometimes get rapidly damaged when prematurely whishing to put the road way back into service. To counteract these drawbacks, some patents recommend to add catalysts comprising metal salts, but those are to be avoided to respect the environment
The French patent application FR 2 768 150 (SAADA) describes a bitumen binder comprising a fluxing oil selected from fatty acid esters, obtained in particular by vegetable oil transesterification, and preferably a fluxing oil polymerization catalyst. The oils used are methyl esters of rapeseed, linseed or sunflower seed oils, having optionally been previously isomerized.
The isomerization treatment objective is to increase the number of conjugated C═C double bonds, which results in an increase in the drying power.
The conjugated double bonds of the fluxing oil reduce its initial viscosity and play a major role in the binder hardening. Indeed, after spreading, the binder hardening does occur upon crosslinking of the fluxing oil in the presence of the air oxygen and the catalyst (transition metal salts). The metal salts form peroxide —O—O— bridges on the fatty acid unsaturated chains. Such bridges are unstable and lead to the formation of free radicals, which attack other chains, thus producing through propagation a polymerization-crosslinking of the esters.
The French patent application FR 2701021 (SCREG) describes an emulsion comprising a hydrocarbon binder, especially a bitumen, and at least one natural or synthetic, drying oil or semi-drying oil, or at least one stand oil of such an oil and in general one catalyst of the transition metal type used as an accelerating agent, i.e. manganese naphthenate.
Only the European applications EP 1 482 012 and EP 0 4075 882.3 (LATEXFALT B.V.) describe fluxed bituminous binders that do not require to use polymerization catalysts of the transition metal type in order to crosslink the fluxing oil. These binders comprise, in addition to bitumen, an unsaturated fatty acid C1-C4 alkyl ester used as a fluxing oil, an elastomer, a hardening agent to promote the elastomer crosslinking and optionally an amide-type additive intended to further reduce the viscosity of the fluxed bitumen and to increase the softening temperature of the composition.